You might try starting from Fate Points instead of from Aspects. Tell them that fate points are a currency. You get them at the start of an adventure, or when the GM decides to screw you over. You can spend them whenever you want +2 to a roll or a re-roll.
Then, when they try to spend a fate point, let them know that they need to justify it by pointing to an aspect. This leads into the idea that no fate points ever change hands without an aspect involved.
Next, you can bring up the idea of declarations, assessments, and maneuvers in terms of "you can roll to find/create an aspect when there isn't a good one already there" and that the reward for doing so is a free, invisible fate point (called a 'tag') that can only be spent on that newly found/created aspect.